March, 2018:
We have had lots of personal recommendations for this part in the past, calling it perfect fit. That didn't take long to change (quality). I installed a new one procured in March, 2018, and it has the filler neck in wrong location. It is mislocated nearly a half inch toward the right rear corner of the car, so the pipe hits hard on the elliptical opening in the boot floor. I got the mounting straps attached okay (just barely), but had to grind the heck out of the inside of the steel seal retaining ring to get the screw holes to line up. Also move the rubber seal over to fit around the new location of the filler neck, and punch a few more screw holes in the seal for new location. Not good.

Addendum September 2021:
Moss is still selling the faulty parts with filler neck in wrong location. Earlier Moss part number was 456-800, which was the good part. Current Moss part number is 456-801, which is the bad part coming from a different source. Current response from Moss is, "We recommend using a slightly longer hose for the connector pipe". which may get you connected, but does not solve the fitting problem due to misalignment. The implication is that Moss intends to keep on selling these faulty parts, at least until they might deplete inventory, after which the next batch might be better. Don't hold your breath while waiting.

Addendum September 13, 2021:
Someone from Moss Motors "claims" that they have redesigned and ordered new MGA fuel tanks as of late 2020, and any parts currently in stock (Sept 2021) should be new design and will fit properly. I will have to reserve judgement until we can get a field report from a recent buyer. Meanwhile, there may still be some of the older faulty units in stock with some of the Moss parts distributors, so do still keep an eye out for this problem, and feel free to return any tank that does not fit. Do check the new part before you begin to paint of modify it (which may negate the warranty return).